1. Technical Field
The invention relates to a hologram-recording material using hologram recording suitable for large-capacity information recording, a hologram-recording medium using the same, and a hologram-recording method using the hologram-recording medium.
2. Related Art
In holographic data storage, it is possible to record polarized light by selecting polymeric materials having azobenzene skeletons in their molecules that change their orientation between trans and cis isomers by photoirradiation (hereinafter, sometimes referred to as “azopolymers”) as the material for use in hologram recording.
Such polarized light recording allows incorporation of security keys and operations for data, just the sort of distinctive features of recording methods used for hologram recording. However, materials currently studied as recording materials for hologram-recording medium allowing recording of polarized light, such as azopolymers, are researched as rewritable materials, because the photoisomerization reaction occurring therein is reversible and the polarized light recording cannot be preserved for an extended period of time.
On the other hand, a large-volume of information can be recorded by the holographic data storage, and thus, there is a greater need for a write-once hologram-recording medium that will not loose the information once recorded, than for a rewritable hologram-recording medium.
Known hologram-recording media that satisfy such a need include those using photopolymerizable polymer recording materials (so-called photopolymers) that perform recording by using an irreversible reaction, polymerization, caused by photoirradiation. However, such media cannot be used for polarized light recording and do not have the advantages described above. It also has a disadvantage that deterioration in sensitivity becomes more distinctive, as multiple recording is carried out during multiplex recording.
In contrast, there are many known optical recording media using photochromic materials, such as azopolymers, in which photoisomerization reactions occur by photoirradiation.
However, such media is not capable of fixing (preserving) of the information once recorded, and thus, cannot be used as a write-once optical recording medium, because the information previously recorded is lost when it is overwritten with new information.
On the other hand, control of the orientation of molecules such as photochromic materials having an azobenzene skeleton in the field of hologram recording is also important in other fields, such as liquid crystal displays and optical filters, and various research is being undertaken.
However, as described above, there is still no write-once optical recording medium allowing multiplex recording by using polarized light, with high sensitivity during recording, and also, superior in the efficiency of fixing information once recorded.